Ignition systems without breaker points for use with internal combustion engines are well known. Such systems provide an ignition impulse causing a spark in one or more cylinders by either discharging a capacitor to cause a sudden flow of electrical current through the primary of an ignition coil, or by interruption an electrical current through the primary of the ignition coil to discharge its magnetic field, to cause an ignition impulse in the ignition coil secondary. Such systems provide an ignition impulse at a proper time by sensing the position of a rotating element of the internal combustion engine, and providing an ignition advance either electronically or mechanically.
Conventionally, a timing rotor is rotated past a sensing coil or pickup. The trigger rotor is a spider-shaped device, having a plurality of arms, corresponding to the number of cylinders of the internal combustion engine to be operated, the arm being conductive for use with sensing coils, or opaque, for use with photo-electric pick-up. Such spider-shaped structures are conventionally made by molding, by sintering, stamping, or by metal plating on a molded plastic structure. Such interrupted structures are difficult to fabricate, being subject to warpage during forming, as well as having other difficulties corresponding to the method of manufacturing. For example, stamping and sintering both become more difficult when depth and thickness ratios between ajoining elements become large. Metallic plating on non-conductive rotating elements may peel off.
Establishing and maintaining relative positioning of a trigger rotor and sensing element is also difficult. It is particularly difficult in applications where the trigger rotor and sensing coil are moved in respect to each other in the process of establishing initial engine timing, such as with internal combustion engines such as used on some motorcycles.
The use of mechanical advance systems is also known. Such advance systems may include centrifugal weights, which have pins which slidably protrude through a plate attached to a breaker point cam, or a cam-shaped element, for use with an electronic ignition system pickup coil, or have protrusions from centifugal weights which slide in a groove in the member carrying the cam. In order to obtain a dual-sloped advance, unequal springs on two weights are conventionally used. One spring is selected so that is always restrains one weight, while another spring is selected so that it begins to restrain the other weight after the engine reaches a predetermined speed, giving an ignition advance dependent on only one spring up to a predetermined speed. In practice, this means that, below the predetermined speed, one spring is restraining both the weight to which it is attached and the weight that is not yet being restrained by the second spring. This creates frictional forces, which leads to hysteresis, or, a different amount of advance for a given engine speed when the engine is decelerating than when it is accelerating.
Therefore, it is the first objective of the invention to provide a structure for an ignition controller which insures and maintains correct positioning between a trigger rotor and a sensing coil. It is a feature of this first objective that a stationary carrier for the sensing coil rotatably engages the rotating shift which carries the trigger rotor, whereby the trigger rotor and the sensing coil are referenced to the shaft and to each other. It is advantage of this first objective that the radial relationship between the trigger rotor and sensing coil cannot be disturbed when the sensing coil is moved angularly to establish initial ignition timing.
It is a second objective to provide a trigger rotor in the form of a disk with two protruding parallel walls forming a groove, with a conductive element disposed within the groove. It is a feature of this second objective that a metallic element disposed within the groove is a generally U-shaped metal channel member comforming to, and embedded in, the surface of the disk and two walls. It is an advantage of this trigger rotor that it is without separate arms which may strike and damage a sensing coil, particularly when the rotor and sensing coil are manually moved with respect to each other, a further advantage being that the trigger rotor is relatively easy to manufacture by molding, with as many metal channel members as desired being placed in a mold before injection of plastic, thereby being adaptable to an engine with any numbers of cylinders, as well as being resistant to warpage during or after manufacture.
It is a third objective of the invention to provide an advance mechanism which utilizes a rolling contact between elements to reduce frictional wear. It is a feature of this objective that rolling contact is produced by providing a projection on centrifugal weights in the form of a gear tooth, cooperating with gear teeth formed in the trigger rotor. This produces the advantage that long life and accurate ignition advance can be obtained.
It is further objective of the invention to provide a spring arrangement for a centrifugal advance mechanism that does not provide unequal forces. It is a feature of this objective that two weights are provided with substantially identical restraining springs, active simultaneously, the weights being further restrained by a separate, self centering, dual-ended spring which is contacted by the centrifugal advance weights when the associated engine reaches a predetermined speed. The advantage of this spring arrangement is the elimination of non-symmetrical forces which cause hysteresis in advance curves, and also provides independent control over the slope of the advance curve above a predetermined speed.